A derelict Georgian mansion has been rescued with a full period-correct restoration and the addition of a new glulam-timber extension to provide Dorset with a new arts venue. The project used a JCT Standard Building Contract.
Sherborne House in Dorset is a Grade I listed building which features Georgian, Tudor, and medieval elements. The main structure is an early Georgian mansion which has been attributed to local architect and craftsman Benjamin Bastard. Its principal staircase features an original mural depicting hunting scenes completed in the 1720s by Dorset-born artist James Thornhill, who is best known for the paintings inside the dome of St Paul’s Cathedral.
The house was a private home until 1931, when it was purchased by Dorset County Council to house Lord Digby’s School for Girls. By the end of the school’s tenure in 1992, the building had not been well maintained and, after remaining empty for the intervening years, was placed on Historic England’s Heritage at Risk Register due to the building becoming dilapidated.
In 2018 the building was purchased by the Sherborne House Trust – an independent charitable trust set up to restore the building, preserve the Thornhill mural, and create a centre to widen participation in, and accessibility to, the arts.
Planning permission was granted in 2021 and the project, renamed The Sherborne, was ready to undergo a full restoration and extension. SPASE architects were engaged to design the project. The completed build offers the following new features:
- Gallery spaces in both historic rooms and new-build extension
- A sculpture garden and external amphitheatre for live performances at the rear
- A bistro and restaurant, event spaces for hire, and a shop stocking local products – with profits supporting the arts programme.
The carrying out of the works can be described in two distinct sections, the restoration of the existing building, and the newly built extension.
Restoration
Despite the building being watertight, it was in serious need of structural repair. Extensive works were carried out to stabilize the floors, ceilings and walls in as discreet a way as possible, with the aim that most visitors would never fully notice the extent of the repairs carried out. Specialists from Mann Williams structural engineers were engaged to complete the works on the historic parts of the building.
Careful research, repair, and conservation has been carried out to ensure that the restoration works were as historically accurate as possible. Works included replacing and repairing Georgian panelling, installing new timber doors where existing ones were missing, restoring fireplaces and decorative finishes, as well as removing inappropriate paint finishes. Lime plasters were taken for laboratory analysis to ensure repairs were undertaken with the correct mixes, and specialist decorators have created an interior scheme based on a 1726 inventory. The whole exterior has been meticulously cleaned and hand-painted to ensure a seamless blend between the original stone and the new lime renders.
Textiles, such as bespoke silks and carpets, have been woven in Suffolk and Yorkshire to historical designs and specifications. The painting on the mural has been fully restored, alongside the joinery of the staircase so that the entire scheme is much closer to that completed by James Thornhill in the 1720s. A new bespoke lighting scheme ensures that the mural is displayed properly, with ‘candlelight’ temperature lighting.
As a result, the building has been removed from the Heritage at Risk Register.
New Build
At the outset of the project, it was clear that the existing building would not be viable on its own to meet the ambitions of what the scheme wanted to achieve. However, the planned extension, which doubles the size of the overall footprint, needed to be sensitively handled to make sure the history of the existing building was appropriately respected and protected.
It was decided to extend to the northern (rear) of the site with single-storey structures that wrap around a central courtyard – providing separation from the main building. The primary structure is a new pavilion – a glulam-timber building sourced from sustainable spruce. It is 22-feet high, and its self-supporting roof structure and ceiling is formed of 17-metre pieces of laminated European spruce, each weighing 1.5 tonnes. It features concave sculpted copper-clad roofs that are designed to assist the flow of passive ventilation.
Further sustainable measures have been implemented with the use of wood-fibre ventilation, complementing the upgrade to the existing building, whose thermal performance was improved with the use of breathable hemp in the roofs and intermediate floors, as well as recycled foamed glass under new limecrete floor slabs. Air source heat pumps have been introduced alongside mechanical ventilation heat recovery. A future phase is planned to install photovoltaic panels.
The pavilion provides a marked contrast to the existing building, but it achieves a sensitive balance between celebrating its own very contemporary features and complementing the historic building. The colour scheme of the natural spruce and copper roofs is brought together with the stone of the mansion, and the floor-to-ceiling glazing of the pavilion provides a harmonious link between the gardens and main building, enabling it to be fully appreciated with views from the courtyard aspect.
With a mix of conservation, restoration, new-build, and some complex technical construction, involving a variety of specialist disciplines, a project of this nature requires a contract capable of capturing complex requirements and making sure the responsibilities of all parties is clear. The JCT Standard Building Contract is a benchmark in the industry for providing a reliable and well-established document, that has enabled the building of many such projects. As with The Sherborne, it is just as capable as mixing the traditional and the contemporary.
Project Data
Start on site: November 2021
Completion: May 2024
Gross internal floor area: 2640m2, (existing: 1622.5m2, new: 1017.5m2)
Contract: JCT Standard Building Contract
Client: Sherborne House Trust 2018
Architect: SPASE Architects + Surveyors
Main contractor: Stonewood Builders
Structural engineer Mann Williams
M&E consultant: QODA
Quantity surveyor: PGP
Landscape consultant: SPASE Architects + Surveyors
Soft landscaping: Angela Morley
Acoustic consultant: Sol Acoustics
Principal designer: SPASE Architects + Surveyors
Approved building inspector: LABC
CAD software used: AutoCAD
Image: Brett Charles